The use of brush seals for sealing gaps, such as those found in gas turbine engines, is known in the art. For example, in gas turbine engines brush seals are often utilized to minimize leakage of fluids at circumferential gaps, such as between a machine housing and a rotor, around a rotary shaft of the engine, and between two spaces having different fluid pressure within the engine. The fluid pressure within the system, which may be either liquid or gas, is greater than the discharge pressure (the pressure outside the area of the engine housing, toward which the fluid will tend to leak), thus creating a pressure differential in the system. As used herein, the system pressure side of the brush seal is referred to as the high pressure side, while the discharge pressure side of the brush seal is referred to as the low pressure side.
Conventional brush seals include a bristle pack which is held and guided at one end between a retaining plate and a back plate. The bristle pack is preferably flexible and includes a plurality of bristles for sealing the gap, the bristles having a free end for contacting one component, such as the rotor. While the retaining and back plate provide support for the bristle pack, they also add weight, which is not advantageous. The bristle pack is welded to the retaining plate and back plate so that the bristles do not come loose during use. Conventional designs utilize a weld pool large enough to hold the bristles to the retaining and back plates, the weld pools being critical in preventing the bristle packs from coming loose during use since they are often the only thing holding the bristle packs in place. Circular brush seals have been utilized in gas turbine engine applications to minimize leakage and increase engine fuel efficiency. Properly designed brush seals can seal up to several hundred psi of differential pressure, at surface speeds exceeding about 1000 ft/sec., and at temperatures up to about 1500 degrees F.
One style brush seal is disclosed in U.S. Pat. No. 5,066,024 to Reisinger et al. The Reisinger brush seal 1 includes a wire bundle 2 that is wound in a U-shape and bent around a core ring 8. The core ring is bent to the appropriate radius and is captured within a curved or ring-shaped tube 3 which includes a continuous slot. In its bent area, the wire bundle 2 is contacted and surrounded by the tube 3. The tube 3 is enclosed on both sides and tensioned by a pair of support rings 4 and 5 which are joined by welding at a welding joint 9 to form a housing. The joined support rings provide the required clamping force to the wire bundle 2 via the tube. In this design, the slotted tube which directly surrounds the brushes only provides for the protection of the bristles, while the required clamping force is provided solely by the joined support rings.
Another style brush seal is disclosed in U.S. Pat. No. 5,794,938 to Hofner et al. The Hofner brush seal 1 includes a plurality of stacked bristles 2 which are clamped in a U-shape around an annular core ring 3 by clamping ring 4. The clamping ring 4 is secured in an annular space U, formed between two housing portions 5a, 5b of stator 6. The legs of the bristles extend through an annular slot 7 in the clamping ring 4, towards a rotor 9. The clamping ring 4 includes a C-shaped section which clamps the bristles 2 against the core ring 3, and reverse bend portions 8a, 8b at opposite ends of the C-shaped section between which the slot 7 is formed. The C-shaped section 10 of the clamping ring 4 clamps the bristles 2 against the core ring 3 concentrically with the C-shaped section. The reverse bend portions 8a, 8b each extend into outwardly projecting radial anchor portions which form the backing elements 12a and 12b that tangentially contact the C-shaped section 10. The brush seal 1 is mounted in the stator by clamping the backing elements 12a and 12b between the housing portions 5a and 5b of the stator 6.
While generally acceptable, conventional brush seals are often expensive to produce, and are often complicated to manufacture. In addition, brush seals are subject to considerable wear and, in conventional designs, are often difficult and costly to replace.
Accordingly, there is needed in the art a brush seal which is inexpensive and easy to manufacture, and which can be readily replaced once worn.